Activation of steroid receptors regulates gene transcription which causes changes in neuronal activation and ultimately behavior, therefore an understanding of cellular processes regulating steroid receptor concentrations has clinical importance. A recent study has shown that mating causes down-regulation of progestin receptors in some brain areas. Mating-induced potentiation of lordosis in estrogen-primed female rats appears to be the result of ligand- independent activation of progestin receptors, because the effect can be blocked by a progesterone antagonist in the absence of progesterone. It is hypothesized that mating-induced down- regulation of progestin receptors is also mediated by ligand- independent activation of progestin receptors. In the present series of experiments, the cellular mechanisms mediating mating- induced down-regulation of progestin receptors will be explored. In addition, these experiments will provide more extensive training in steroid receptor immunocytochemistry, training in intra- cerebroventricular administration of drugs, and training in in situ hybridization.